It's been years since I posted this. I'm not personally supporting this any more, but wanted to mention a few things that happened to it over the years.
There are now severial versions out in the wild - many with improvements and fixes. Some are mentioned below. However, one thing I want to mention is that I heard that the Modified LiquidCrystal_I2C lib is no longer working. It's just the LiquidCrystal_I2C lib with the "Wire" include defined out. The newer version of this lib can be easily modified to make it work.
On a personal note, I was very happy to see how useful these libs have become. However, it would have been nice if someone really built on my naive attempt and made these libs what they should be. Oh well.
The ATtiny85 microprocessor is an 8 pin chip with 6 (max!) I/O ports. Using an I2C bus greatly expands the possibilities of what you can do with this chip.
The ATtiny85 (and it's cousins) does not have I2C (or SPI) "built in". Instead it has a Universal Serial Interface (USI) that can be used to facilitate I2C and SPI.
After a bit of searching, I found 2 sets of code that use the USI for I2C - one for I2C master and the other for I2C slave. I wrapped each in a separate class and had them follow a similar usage as the Wire lib.
I don't consider myself a "sharp guy" when it comes to coding, and this was my first experience with making a class, so go easy. As far as I'm concerned, these libraries are done. However it would be nice to see the master and slave libraries combined like the Wire library is. The slave lib is also missing the "onReceive" and "onRequest" functions - however it is still usable.
I've only tested these libraries with an ATtiny85. They may work on an ATtiny45 and others that use USI with easy mods to the include files.
Testing was done using the the ATtiny85 core files from "high-low tech" http://hlt.media.mit.edu/wiki/pmwiki.php?n=Main.ArduinoATtiny4585 and also the core files from http://code.google.com/p/arduino-tiny/ and uploaded with the ArduinoISP or the USBtinyISP.
Both the 1MHz and 8MHz clock speeds were tested.
Each library includes examples, and there is documentation in the headers of these, and more in the associated .h files.
The base code for this lib came from 'jkl' at CMU - see .h for link. I've tested send and receive on severial I2C devices. You can download the lib here: TinyWireM.zip
USAGE is modeled after the standard Wire library . . . Put in setup(): TinyWireM.begin(){ // initialize I2C lib To Send: TinyWireM.beginTransmission(uint8_t slaveAddr){ // setup slave's address (7 bit address - same as Wire) TinyWireM.send(uint8_t data){ // buffer up bytes to send - can be called multiple times someByte = TinyWireM.endTransmission(){ // actually send the bytes in the buffer // returns (optional) 0 = sucess or see USI_TWI_Master.h for error codes To Receive: someByte = TinyWireM.requestFrom(uint8_t slaveAddr, uint8_t numBytes){ // reads 'numBytes' from slave's address // (usage optional) returns 0= success or see USI_TWI_Master.h for error codes someByte = TinyWireM.receive(){ // returns the next byte in the received buffer - called multiple times someByte = TinyWireM.available(){ // returns the number of unread bytes in the received buffer
(:sourcend:)
The base code for this lib came from Don Blake at AVR freaks - see .h for link. I've tested receive and respond while connected to a "master send a receive" sketch on the Arduino. You can download it here: TinyWireS.zip
USAGE is modeled after the standard Wire library . . . Put in setup(): TinyWireS.begin(I2C_SLAVE_ADDR); // initialize I2C lib & setup slave's address (7 bit - same as Wire)
To Receive:
someByte = TinyWireS.available(){ // returns the number of bytes in the received buffer
someByte = TinyWireS.receive(){ // returns the next byte in the received buffer
To Send:
TinyWireS.send(uint8_t data){ // sends a requested byte to master
(:sourcend:)
After becoming quite tired of counting flashing LEDs on the ATtiny, I made a small mod to Mario H's LiquidCrystal_I2C library that will use TinyWireM instead of Wire when compiling for an ATtiny85. It's pretty cool to see a 2x16 LCD display running from that tiny chip! I added an example "HelloWorld_Tiny" to his examples. You can download the modified LiquidCrystal_I2C library for the ATtiny here: LiquidCrystal_I2C_85V1.zip (v1+ IDE)
This lib still supports the ATmega as it always had, so you can safely replace your LiquidCrystal_I2C lib with this one.
I hope you find these libraries fun and useful.
(Blog with I2C/85 project - http://brohogan.blogspot.com/search/label/ATtiny85)
I have implemented onRequest and onReceive (with limitations) support, get the files from my Github repository https://github.com/rambo/TinyWire/blob/master/TinyWireS/ and check out example attiny_i2c_slave.ino
This version also includes improvements from others that I have found when trying to solve my issues with the original library.
If you need support for the ATtiny84 (or 44), there is a forked version of the above library on Github that supports the ATtiny44/84 series. https://github.com/svoisen/TinyWire
I united the TinyWireM and TinyWireS libraries to get master and slave functionality in one library. It is now possible to init the library as slave and sending as temporary master (and being a slave again after it). With this, the library behaves a bit more like the Wire library. As in the latest version of the TinyWireS library, you can use the onRequest and onReceive user callback and the library implements bus arbitration (it just doesn't check on arbitration lost, if it was addressed itself). It should also implement correct slave clock streching (see issue #1). For supporting other than ATTiny25/45/85 you only have to fill in the device dependent definitions in the library. You can find the library on https://github.com/lucullusTheOnly/TinyWire